Field of the Invention
This invention relates generally to fouling deterrence.
Background
Biofouling or biological fouling is the undesirable accumulation of micro-organism, plants, algae, and animals on submerged structures, especially ships' hulls. Biofouling also occurs on the surfaces of living marine organisms, when it is known as epibiosis.
The control of biofouling on artificial surfaces is a significant problem for structures in contact with the marine environment. Historically, anti-biofouling coatings utilized biocides that leach out from the coating over time to thereby prevent biofouling settlement by virtue of the biocides toxicity to marine organisms. This method of control has had a number of problems associated therewith. First, the biofouling resistance of the coating decreases with time as the biocides are depleted by their leaching out. Furthermore, the toxic coatings increase the danger of toxic exposure to shipyard workers, create a hazardous waste disposal problem, and have a detrimental environmental impact on marine wildlife. Subsequent to the removal of environmentally hazardous organo-tin compounds from antifouling paints, control of biofouling accumulation has become the single most expensive maintenance problem incurred by the U.S. Navy for ship operations.
The need for anti-biofouling methods is evident in U.S. Department of the Navy, NAVSEA'S coating needs, which are based on criteria such as environmental drivers (copper-free or low copper (UNDS limits pending)), cost drivers (up front cost and maintenance (313 Ship Navy)) and operational cost (12-year dry docking interval and minimal in-service cleaning).
Along the coasts of the North Atlantic Ocean, barnacles and different kinds of algae are particularly apparent problems. The fully grown barnacle is a stationary crustacean (arthropod), characterized by a centimeter-sized cone shape and enclosing layers of calcinous plates. The mechanical strength of the animal's attachment to solid surfaces is very high, and it is therefore difficult to mechanically remove barnacles from solid surfaces. The animal undergoes different development stages as free-swimming larvae, where the last larva stage is referred to as the cyprid stage. The cyprid screens solid surfaces suitable for settling with the help of a nervous protuberance, the antennule. A “settling-glue” referred to as balanus cement is secreted from specialized glands localized near the protuberance and the animal thereby settles to the solid surface. After settlement the animal undergoes a metamorphosis into an adult and stationary animal.
The common name oyster is used for a number of different groups of bivalve mollusks, most of which live in marine habitats or brackish water. The shell consists of two usually highly calcified valves which surround a soft body. Gills filter plankton from the water, and strong adductor muscles are used to hold the shell closed. Oysters are a biofouling species. The pediveliger larva is last larval stage of an oyster in which the veliger larva (characterized by a ciliated lobe (or lobes) known as the velum which functions in propulsion and food-gathering) develops a foot and seeks a substrate on which to settle. The settling and cementation process leads to biofouling of the substrate.